Investigation of silicate mineral sanidine by vibrational and NMR spectroscopic methods

Sanidine, a variety of feldspar minerals has been investigated through optical absorption, vibrational (IR and Raman), EPR and NMR spectroscopic techniques. The principal reflections occurring at the d-spacings, 3.2892, 3.2431, 2.9022 and 2.6041 Å confirm the presence of sanidine structure in the mineral. Sanidine shows five prominent characteristic infrared absorption bands in the region 1200–950, 770–720, 590–540 and 650–640 cm−1. The Raman spectrum shows the strongest band at 512 cm−1 characteristic of the feldspar structure, which contains four membered rings of tetrahedra. The UV–vis–NIR absorption spectrum had strong absorption features at 6757, 5780 and 5181 cm−1 due to the combination of fundamental OH– stretching. The bands at 11236 and 8196 cm−1and the strong, well-defined band at (30303 cm−1 attest the presence of Fe2+ and Fe3+, respectively, in the sample. The signals at g = 4.3 and 3.7 are interpreted in terms of Fe3+ at two distinct tetrahedral positions Tl and T2 of the monoclinic crystal structure The 29Si NMR spectrum shows two peaks at −97 and −101 ppm corresponding to T2 and T1, respectively, and one peak in 27Al NMR for Al(IV).